Avidin is a glycoprotein, which occurs in egg white and is well known because of its property of binding to biotin, with an association constant of 1015 M−1, the highest known for a bioaffinity pair.
Eatkin et al (1940) and Pennington et al. (1942) reports presence of Avidin and isolation in crude form. Conrat et al. (1952) reports very tedious and multi-step process for the isolation of Avidin by involving salt precipitation and adsorption on Bentonite. The above references are pertaining to early days when Avidin was not even characterized at the molecular level.
N. M. Green (1965) screened several anionic dyes for studying binding to Avidin and examined spectroscopically. The most striking results were obtained by using 4′-hydroxyazobenzene-2-carboxylic acid (HABA). Green et al. (1970) describe a multi-step process for the isolation of Avidin involving considerable amount of time. Bayer and Wilchek, (1974) used affinity chromatography on biocytin (ε-N-biotinyl-L-lysine)-linked matrices for the purification of Avidin. Since the association constant with biocytin is very high, 6-M guanidine hydrochloride of pH 1.5 was used for elution. This resulted in poor and irreproducible results. Wilchek and Bayer, (1988) have described Avidin in enzyme-linked immunosorbent assay (ELISA), immunochemical staining, electron microscopy and affinity chromatography.
U.S. Pat. No. 4,966,851 describes the isolation of Avidin using weakly acidic ion-exchanger resin from egg-white by employing stepwise elution with buffer to obtain Avidin having a very low purity of about 12%. Thus, the process leads to non-specific recovery of target protein.
All the prior art processes described earlier involve either multi-step isolation or poor purity of Avidin. The present invention describes a quick, economical, efficient and a single step process for the isolation of Avidin from egg white. Also, the present process has a distinct feature of HABA being used as an eluant to carry out desorption of Avidin from the solid matrix cation exchanger used in the isolation process in comparison to the prior art processes wherein HABA has been always covalently bonded to the solid matrix and the covalently bonded conjugate is in turn used in the process for the isolation of Avidin.